By Sam Kim SEOUL, Oct. 22 (Yonhap) -- The U.S. pledged Thursday to mobilize its warfighting assets to their maximum capacity if needed to defend South Korea against North Korea, which continues to develop its nuclear and missile capabilities.

U.S. Secretary of Defense Robert Gates "reaffirmed the U.S. commitment to provide extended deterrence for the ROK, using the full range of military capabilities, to include the U.S. nuclear umbrella, conventional strike, and missile capabilities," according to a joint statement with South Korean Defense Minister Kim Tae-young.

ROK stands for the Republic of Korea, South Korea's official name.

The affirmation constitutes the latest in a series of warnings from the U.S. to North Korea that defied international warnings and went ahead with its second nuclear test in May.

"North Korea's emerging nuclear weapons programs have a destabilizing effect both regionally and internationally," Gates told a joint press conference following his three-hour-long talks with Kim.

The U.S. has 28,500 troops stationed here as a legacy of the 1950-53 Korean War, which ended in a truce rather than a peace treaty.

Following the annual Security Consultative Meeting in Seoul, Kim said the allies are examining "all possible scenarios" that may arise in North Korea."

"I can say our interest in this matter is very serious and the details are being looked at very closely," he said, raising concern over "chronic economic hardships" facing North Korea.

North Korea is believed to be undergoing a power succession after leader Kim Jong-il suffered a stroke last year. The 67-year-old has apparently recovered enough to reassert his power over the regime.

"In regards to the contingencies and unstable situations, the ROK and the United States will do all they can to make sure there are no negative effects as a result of such events to the peace on the Korean Peninsula," Kim said.

"In order to do that, we are currently looking into all possible scenarios and developing plans," he said. The SCM is alternately held in Washington and Seoul each year.

The comments by the two ministers coincided with those of U.S. Secretary of State Hillary Clinton, who warned earlier that North Koreans "should have no illusion that the United States will ever have normal, sanctions-free relations with a nuclear-armed North Korea."

"Current sanctions will not be relaxed until Pyongyang takes verifiable, irreversible steps toward complete denuclearization," she said at a forum in Washington.

Gates, who flew to Europe for a NATO meeting after ending the second leg of his two-nation Asian trip, said he has made "no specific request during my visit here in terms of Afghanistan."

"It is entirely up to the government of the Republic of Korea what it chooses to do in Afghanistan," he said. "There are a range of needs from helping to pay for the expansions and sustainment of Afghan army and police. There are civil projects and economic reconstruction and so on."

"So we obviously welcome any contribution that any countries around the world are prepared to make, but that decision -- what and how much to contribute -- is entirely up to the Republic of Korea," he said.

South Korean media have speculated for weeks that the visit by Gates is aimed at paving the ground for U.S. President Barack Obama to ask his South Korean counterpart, Lee Myung-bak, to send combat troops to Afghanistan when he visits Seoul next month.

The joint communique marked the first time that the U.S. has expanded on the concept of "extended deterrence," which was stipulated in a summit agreement between Obama and Lee in June in Washington.

It came even as North Korea appeared willing to engage in dialogue with the broader world while showing no signs of backing down in its nuclear and missile development.

The country recently resumed the testing of its short-range missiles for the first time in more than three months, while warning of a naval clash off the west coast of the divided Korean Peninsula.

"On the surface, there are signs of some change from North Korea, including its recent willingness to talk. In reality, the unstable situation such as its nuclear program and military-first policy continues unchanged," Kim told Gates during an earlier meeting.

The communique reaffirmed that the allies will not accept North Korea coming to the bargaining table while being recognized as a country armed with nuclear arms.

"The Minister and the Secretary reiterated that the ROK and the U.S. will not accept North Korea as a nuclear weapon state," it said.